Assigning variables in on_[macosversion] blocks

[unitof]

Output of brew config

n/a

Output of brew doctor

n/a

Description of issue

The audio application developer Rouge Amoeba has been gradually updating their applications (Piezo, Audio Hijack, Loopback) to support macOS's new Audio Routing Kit framework for less invasive installation. ARK is available on macOS 14.5 and later. For macOS 14.4.x and below, Rogue Amoeba is continuing development a separate version track of each app using their legacy ACE audio engine, typically one minor version below the ARK version but with identical functionality.

The Casks now have a number of largely repeated stanzas and strings, especially the url and livecheck, and was hoping to do something like the pattern we often do with livecheck_folder and on_arch_conditional, but I don't see any conditionals similar to on_arch_conditional for macOS versions.

Is the below permissible? Is there a nicer way to do it? It passes audit and style, but no other casks define variables as empty strings up top, so I assume it is discouraged and ugly.

cask "loopback" do
  sha256 :no_check

  macosversion_no_dots = ""
  audio_engine = ""

  on_ventura :or_older do
    # macOS 11.0 is oldest supported version
    macosversion_no_dots = "110"
    audio_engine = "ace"

    version "2.3.3"
  end
  on_sonoma :or_newer do
    macosversion_no_dots = "145"
    audio_engine = "ark"

    version "2.4.0"
  end

  url "https://rogueamoeba.com/loopback/download-#{audio_engine}.php"
  name "Loopback"
  desc "Cable-free audio router"
  homepage "https://rogueamoeba.com/loopback/"

  livecheck do
    url "https://rogueamoeba.net/ping/versionCheck.cgi?format=sparkle&system=#{macosversion_no_dots}&bundleid=com.rogueamoeba.Loopback&platform=osx&version=#{version.no_dots}8000"
    strategy :sparkle
  end

  # code omitted

end

For now, I have defined url and livecheck for each on_[macosversion] block, in full: https://github.com/Homebrew/homebrew-cask/pull/176100/files

[SMillerDev]

I would put the newest version by default and override in only one block